Anode active material and secondary battery comprising the same

ABSTRACT

Disclosed are an anode active material for secondary batteries, capable of intercalating and deintercalating ions, comprising a core comprising a crystalline carbon-based material and a composite coating layer comprising one or more materials selected from the group consisting of low crystalline carbon and amorphous carbon, and a metal and/or a non-metal capable of intercalating and deintercalating ions, wherein the composite coating layer comprises a matrix comprising one component selected from one or more materials selected from the group consisting of low crystalline carbon and amorphous carbon and a metal and/or a non-metal capable of intercalating and deintercalating ions, and a filler comprising the other component, incorporated in the matrix, and a secondary battery comprising the anode active material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/KR2011/009172 filed on Nov. 29, 2011, which claims priority under 35U.S.C. §119(a) to Patent Application No. 10-2010-0135417 filed in theRepublic of Korea on Dec. 27, 2010, all of which are hereby expresslyincorporated by reference into the present application.

TECHNICAL FIELD

The present invention relates to an anode active material and asecondary battery comprising the same. More specifically, the presentinvention relates to an anode active material for secondary batteries,capable of intercalating and deintercalating ions, comprising: a corecomprising a crystalline carbon-based material; and a composite coatinglayer comprising one or more materials selected from the groupconsisting of low crystalline carbon and amorphous carbon, and a metaland/or a non-metal capable of intercalating and deintercalating ions,wherein the composite coating layer comprises: a matrix comprising onecomponent selected from one or more materials selected from the groupconsisting of low crystalline carbon and amorphous carbon, and a metaland/or a non-metal capable of intercalating and deintercalating ions;and a filler comprising the other component, incorporated in the matrix.

BACKGROUND ART

Technological development and increased demand for mobile equipment haveled to rapid increase in the demand for secondary batteries as energysources. Among these secondary batteries, lithium secondary batterieshaving high energy density and voltage, long cycle span and lowself-discharge are commercially available and widely used.

In addition, increased interest in environmental issues has broughtabout a great deal of research associated with electric vehicles, hybridelectric vehicles and plug-in hybrid electric vehicles as alternativesto vehicles using fossil fuels such as gasoline vehicles and dieselvehicles which are main causes of air pollution. These electric vehiclesgenerally use nickel-metal hydride (Ni-MH) secondary batteries as powersources. However, a great deal of study associated with use of lithiumsecondary batteries with high energy density, discharge voltage andpower stability is currently underway and some are commerciallyavailable.

A lithium secondary battery has a structure in which a non-aqueouselectrolyte comprising a lithium salt is impregnated into an electrodeassembly comprising a cathode and an anode, each comprising an activematerial coated on a current collector, and a porous separatorinterposed therebetween.

Lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide,lithium composite oxide and the like are generally used as cathodeactive materials of lithium secondary batteries and carbon-basedmaterials are generally used as anode active materials thereof and useof silicon compounds, sulfur compounds and the like is also considered.

However, lithium secondary batteries have various problems, inparticular, problems associated with fabrication and driving propertiesof an anode.

First, regarding fabrication of an anode, a carbon-based material usedas an anode active material is highly hydrophobic and thus has problemsof low miscibility with a hydrophilic solvent in the process ofpreparing a slurry for electrode fabrication and low dispersionuniformity of solid components. In addition, this hydrophobicity of theanode active material complicates impregnation of highly polarelectrolytes in the battery fabrication process. The electrolyteimpregnation process is a kind of bottleneck in the battery fabricationprocess, thus greatly decreasing productivity.

In order to solve these problems, addition of surfactant as an additiveto an anode, an electrolyte or the like is suggested. However,disadvantageously, the surfactant may have side effects on drivingproperties of batteries.

Meanwhile, regarding driving properties of anode, disadvantageously, thecarbon-based anode active material induces initial irreversiblereaction, since a solid electrolyte interface (SEI) layer is formed onthe surface of the carbon-based anode active material during an initialcharge/discharge process (activation process), and battery capacity isreduced due to exhaustion of the electrolyte caused by removal(breakage) and regeneration of the SEI layer during a continuouscharge/discharge process.

In order to solve these problems, various methods such as formation ofan SEI layer through stronger bonding, or formation of an oxide layer onthe surface of the anode active material have been attempted. Thesemethods have properties unsuitable for commercialization such asdeterioration in electric conductivity caused by the oxide layer anddeterioration in productivity caused by additional processes. Also,there still exists a problem in that growth of dendrite lithium on thesurface of the anode active material may still cause short-circuit.

Accordingly, there is an increasing need for secondary batteries capableof solving these problems.

DISCLOSURE Technical Problem

Therefore, the present invention has been made to solve the above andother technical problems that have yet to be resolved.

As a result of a variety of extensive and intensive studies andexperiments to solve the problems as described above, the presentinventors discovered that, when an anode active material is produced byforming a composite coating layer on a crystalline carbon-based core,various problems associated with anode fabrication process and batterydriving properties can be simultaneously solved. The present inventionhas been completed, based on this discovery.

Technical Solution

In accordance with one aspect of the present invention, provided is ananode active material for secondary batteries, capable of intercalatingand deintercalating ions, comprising: a core comprising a crystallinecarbon-based material; and a composite coating layer comprising one ormore materials selected from the group consisting of low crystallinecarbon and amorphous carbon, and a metal and/or a non-metal capable ofintercalating and deintercalating ions, wherein the composite coatinglayer comprises: a matrix comprising one component selected from one ormore materials selected from the group consisting of low crystallinecarbon and amorphous carbon, and a metal and/or a non-metal capable ofintercalating and deintercalating ions; and a filler comprising theother component, incorporated in the matrix.

As such, the anode active material having a structure in which the corecomprising a crystalline carbon-based material is coated with thecomposite coating layer having a matrix/filler structure comprising oneor more materials selected from the group consisting of low crystallinecarbon and amorphous carbon, and a metal and/or a non-metal capable ofintercalating and deintercalating ions can solve the problems in therelated art, based on specific active material structure and components.

First, the surface of the metal and/or non-metal capable ofintercalating and deintercalating ions comprised as a matrix or fillercomponent in the composite coating layer is at least partially exposedon the surface of the anode active material and is oxidized, thusbecoming more hydrophilic. Accordingly, the metal and/or non-metalcapable of intercalating and deintercalating ions exhibits highmiscibility with a hydrophilic solvent in a slurry for fabrication of ananode according to the type of materials used, thus improvingdispensability in solid components in the slurry. Accordingly, when ananode is fabricated by applying this slurry to a current collector,distribution uniformity between components such as binder and the anodeactive material can be improved and superior electrode properties canthus be obtained.

The improvement in uniformity of the metal and/or non-metal capable ofintercalating and deintercalating ions can minimize a decrease inbonding strength between the slurry and the partial current collectorwhich occurs on the non-uniform electrode. The metal and/or non-metalcapable of intercalating and deintercalating ions improves affinitybetween the active material layer and the surface of the currentcollector, bonding strength between the active material layer and thecurrent collector and thereby solves a problem of increase in internalresistance caused by separation of the active material layer from thecurrent collector.

Similarly, the metal and/or non-metal capable of intercalating anddeintercalating ions comprised in the composite coating layer impartsrelatively high hydrophilicity to at least a part of the anode activematerial, thereby greatly reducing impregnation time of the highly polarelectrolyte in the electrode fabrication process and considerablyimproving battery productivity.

Second, the metal and/or non-metal capable of intercalating anddeintercalating ions comprised as a matrix or filler component in thecomposite coating layer minimizes deterioration in electricalconductivity which may be induced by presence of material incapable ofintercalating and deintercalating ions.

Also, in a case of a lithium secondary battery, growth of lithiumdendrites may occur, since the crystalline carbon-based material servingas a core has a similar electric potential to lithium, but this growthcan be inhibited by coating the metal and/or non-metal capable ofintercalating and deintercalating ions on the surface of the crystallinecarbon-based material at a high oxidation-reduction level,

Best Mode

Hereinafter, the present invention will be described in detail.

As described above, the anode active material according to the presentinvention comprises: a core comprising a crystalline carbon-basedmaterial; and a composite coating layer comprising: a matrix comprisingone component (for example, amorphous carbon) selected from one or morematerials selected from the group consisting of low crystalline carbonand amorphous carbon and a metal and/or a non-metal capable ofintercalating and deintercalating ions; and a filler comprising theother component (for example, a metal and/or a non-metal capable ofintercalating and deintercalating ions), incorporated in the matrix.

Generally, a carbon-based material is classified into graphite having acomplete layered crystal structure such as natural graphite, soft carbonhaving a low-crystalline layered crystal structure (graphene structurein which hexagonal honeycomb shaped planes of carbon are arrayed in alayer form), and hard carbon having a structure in which thelow-crystalline structures are mixed with non-crystalline parts.

In a preferred embodiment, the core component of the present invention,the crystalline carbon-based material may be graphite, or a mixture ofgraphite and low crystalline carbon, and one of the composite coatinglayer components may be low-crystalline carbon, amorphous carbon, or amixture thereof.

Meanwhile, the metal and/or non-metal capable of intercalating anddeintercalating ions, which is another component constituting thecomposite coating layer in the present invention, exhibits relativelyhigh hydrophilicity and polarity to one or more materials selected fromthe group consisting of low crystalline carbon and amorphous carbon andthus improves mix preparation or electrolyte impregnation.

For realization of this improvement, the metal and/or non-metal capableof intercalating and deintercalating ions are preferably exposed in atleast a part of the surface of the composite coating layer.

Also, such hydrophilicity may be derived from inherent properties of themetal and/or non-metal capable of intercalating and deintercalatingions, or partial oxidization of the metal and/or non-metal capable ofintercalating and deintercalating ions during exposure of the metaland/or non-metal to air. That is, the metal and/or non-metal have aparticle shape, while the surface thereof has relatively highhydrophilicity due to bonding to oxygen. This surface oxidization mayoccur upon exposure of the metal and/or non-metal to air in the batteryfabrication process without separate treatment.

Preferably, examples of the metal and/or non-metal include Si, Sn andthe like. This material may be used alone or in combination thereof.

Si may be used as a metal or an alloy for a high-capacity lithiumsecondary battery anode and is not commercially available due to rapidvariation in volume during charge/discharge. However, according to thepresent invention, when Si is used as a composite with one or morematerials selected from the group consisting of low crystalline carbonand amorphous carbon for a coating layer of a graphite core, the effectsdescribed above as well as improvement in anode capacity can beachieved.

Sn may be also used as a metal or alloy for a lithium secondary batteryanode, but is not yet commercially available. However, similar to Si, Snis used as a composite with one or more materials selected from thegroup consisting of low crystalline carbon and amorphous carbon as thecoating layer of the graphite core, the effects described above as wellas improvement in anode capacity can be achieved.

As described above, by using Si and/or Sn which exerts high capacitywhen used as the anode active material for the surface coating layer,high capacity can be obtained as compared to a case in which a generalcarbon-based anode active material is used alone.

In one embodiment, the metal and/or non-metal may be an alloy of Si andSn. There is no particular limitation as to the type and componentcontents of the alloy of Si and Sn so long as the alloy is capable ofintercalating and deintercalating ions.

In the present invention, the structure of the composite coating layermay be determined, depending on components of matrix and filler.

In a first exemplary structure, a filler comprising a metal and/or anon-metal capable of intercalating and deintercalating ions isincorporated in a matrix comprising one or more materials selected fromthe group consisting of low crystalline carbon and amorphous carbon.

In this case, as described above, in order to obtain the effects ofhydrophilicity, the filler comprising a metal and/or a non-metal capableof intercalating and deintercalating ions is preferably exposed in atleast a part of the surface of the composite coating layer.

In a second exemplary structure, a filler comprising one or morematerials selected from the group consisting of low crystalline carbonand amorphous carbon is incorporated in a matrix comprising a metaland/or a non-metal capable of intercalating and deintercalating ions.

In the composite coating layer, since the matrix has a structure,components of which have a continuous phase and the filler has astructure, components of which have independent phases, the content ofthe matrix component is not necessarily greater than the content of thefiller component.

Accordingly, when the metal and/or the non-metal capable ofintercalating and deintercalating ions forms a composite as a matrix,the metal and/or non-metal capable of intercalating and deintercalatingions is exposed in at least a part of the surface of the compositecoating layer, and the anode active material may thus havehydrophilicity, exerting the effects described above.

In the composite coating layer, the content of one or more materialsselected from the group consisting of low crystalline carbon andamorphous carbon, and the content of the metal and/or non-metal capableof intercalating and deintercalating ions are not particularly limitedso long as the intended effects of the present invention (describedabove) can be exerted. In a preferred embodiment, the content of one ormore materials selected from the group consisting of low crystallinecarbon and amorphous carbon may be 10 to 95% by weight, based on thetotal amount of the composite coating layer and the content of the metaland/or non-metal capable of intercalating and deintercalating ions maybe 5 to 90% by weight, based on the total amount of the compositecoating layer.

The amount (coating amount) of the composite coating layer is preferably0.1 to 20% by weight, based on the total amount of the anode activematerial. When the amount of the composite coating layer is excessivelylow or the thickness thereof is excessively small, effects caused byformation of the composite coating layer may not be obtained and, on theother hand, when the amount of the composite coating layer isexcessively high or the thickness thereof is excessively great,disadvantageously, the desired core-composite coating layer structuremay not be formed and capacity may be deteriorated.

The present invention also provides an anode mix comprising the anodeactive material.

The anode mix according to the present invention comprises 1 to 20% byweight of a binder, and optionally comprises 0 to 20% by weight of aconductive material, based on the total weight of the anode mix.

Examples of the binder include polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVdF), cellulose, polyvinyl alcohol,carboxymethylcellulose (CMC), starch, hydroxypropylcellulose,regenerated cellulose, polyvinyl pyrollidone, tetrafluoroethylene,polyethylene, polypropylene, ethylene-propylene-diene terpolymers(EPDM), sulfonated EPDM, styrene butadiene rubbers, fluoro-rubbers,various copolymers, and polymer-saponified polyvinyl alcohol.

Any conductive material may be used without particular limitation solong as it has suitable conductivity without causing chemical changes inthe fabricated battery. Examples of conductive materials includegraphite; carbon blacks such as carbon black, acetylene black, Ketjenblack, channel black, furnace black, lamp black and thermal black;conductive fibers such as carbon fibers and metallic fibers; metallicpowders such as carbon fluoride powder, aluminum powder and nickelpowder; conductive whiskers such as zinc oxide and potassium titanate;conductive metal oxides such as titanium oxide; and polyphenylenederivatives. Specific examples of commercially available conductivematerials may include various acetylene black products (available fromChevron Chemical Company, Denka Singapore Private Limited and Gulf OilCompany), Ketjen Black EC series (available from Armak Company), VulcanXC-72 (available from Cabot Company) and Super P (Timcal Co.).

If desired, a filler is optionally added to inhibit expansion of theanode. Any filler may be used without particular limitation so long asit does not cause adverse chemical changes in the manufactured batteryand is a fibrous material. Examples of the filler include olefinpolymers such as polyethylene and polypropylene; and fibrous materialssuch as glass fibers and carbon fibers.

Other component such as viscosity controller or adhesion promoter may befurther optionally added singly or in combination of two or more types.

The viscosity controller is a component to control the viscosity of theelectrode mix and thereby facilitate mixing of the electrode mix andapplication of the same to a current collector, and is present in anamount of 30% by weight or less, based on the total weight of the anodemix. Examples of the viscosity controller include, but are not limitedto, carboxymethyl cellulose and polyvinylidene fluoride. In some cases,the afore-mentioned solvent may also act as the viscosity controller.

The adhesion promoter is an auxiliary ingredient to improve adhesion ofan active material to a current collector, is present in an amount of10% by weight, based on the binder and examples thereof include oxalicacid, adipic acid, formic acid, acrylic acid derivatives and itaconicacid derivatives.

The present invention also provides an anode for secondary batteries inwhich the anode mix is applied to a current collector.

For example, the anode is produced by adding an anode materialcontaining an anode active material, a binder or the like to a solventsuch as NMP to prepare a slurry, and applying the slurry to an anodecurrent collector, followed by drying and pressing.

The anode current collector is generally fabricated to have a thicknessof 3 to 500 μm. Any anode current collector may be used withoutparticular limitation so long as it has suitable conductivity withoutcausing adverse chemical changes in the fabricated battery. Examples ofthe anode current collector include copper, stainless steel, aluminum,nickel, titanium, sintered carbon, and copper or stainless steelsurface-treated with carbon, nickel, titanium or silver, andaluminum-cadmium alloys. The anode current collector includes fineirregularities on the surface thereof so as to enhance adhesion of anodeactive materials. In addition, the current collectors may be used invarious forms including films, sheets, foils, nets, porous structures,foams and non-woven fabrics.

The present invention also provides a secondary battery comprising theanode and the battery is preferably a lithium secondary battery.

The lithium secondary battery has a structure in which a lithiumsalt-containing non-aqueous electrolyte is impregnated into an electrodeassembly comprising a separator interposed between the cathode and theanode.

For example, the cathode is prepared by applying a cathode activematerial to a cathode current collector, followed by drying and pressingand further optionally comprise other components such as binder orconductive material described above associated with the configuration ofthe anode.

The cathode current collector is generally manufactured to have athickness of 3 to 500 μm. Any cathode current collector may be usedwithout particular limitation so long as it has suitable conductivitywithout causing adverse chemical changes in the fabricated battery.Examples of the cathode current collector include stainless steel,aluminum, nickel, titanium, sintered carbon, and aluminum or stainlesssteel surface-treated with carbon, nickel, titanium or silver. Similarto the anode current collector, the cathode current collectors includefine irregularities on the surface thereof so as to enhance adhesion tothe cathode active material. In addition, the cathode current collectormay be used in various forms including films, sheets, foils, nets,porous structures, foams and non-woven fabrics.

The cathode active material is a lithium transition metal oxidecomprising two or more transition metals as a substance that causeselectrochemical reaction, and examples thereof include, but are notlimited to, layered compounds such as lithium cobalt oxide (LiCoO₂) orlithium nickel oxide (LiNiO₂) substituted by one or more transitionmetals; lithium manganese oxide substituted by one or more transitionmetals; lithium nickel oxide represented by the formula ofLiNi_(1−y)M_(y)O₂ (in which M=Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga,the lithium nickel oxide including one or more elements among theelements, 0.01≦y≦0.7); lithium nickel cobalt manganese composite oxidesrepresented by Li_(1+z)Ni_(b)Mn_(c)Co_(1−(b+c+d))M_(d)O_((2−e))A_(e)such as Li_(1+z)Ni_(1/3)CO_(1/3)Mn_(1/3)O₂ orLi_(1+z)Ni_(0.4)Mn_(0.4)Co_(0.2)O₂ (in which −0.5≦z≦0.5, 0.1≦b≦0.8,0.1≦c≦0.8, 0≦d≦0.2, 0≦e≦0.2, b+c+d<1, M=Al, Mg, Cr, Ti, Si or Y, A=F, Por Cl); and olivine lithium metal phosphate represented by the formulaof Li_(1+x)M_(1−y)M′_(y)PO_(4−z)X_(z) (in which M=transition metal,preferably Fe, Mn, Co or Ni, M′=Al, Mg or Ti, X═F, S or N, −0.5≦x≦+0.5,0≦y≦0.5, and 0≦z≦0.1).

The binder, the conductive material and optionally added components aredescribed associated with the anode above.

The separator is interposed between the cathode and the anode. As theseparator, an insulating thin film having high ion permeability andmechanical strength is used. The separator typically has a pore diameterof 0.01 to 10 μm and a thickness of 5 to 300 μm. As the separator,sheets or non-woven fabrics made of an olefin polymer such aspolypropylene and/or glass fibers or polyethylene, which have chemicalresistance and hydrophobicity, are used. When a solid electrolyte suchas a polymer is employed as the electrolyte, the solid electrolyte mayalso serve as both the separator and electrolyte.

Where appropriate, a gel polymer electrolyte may be coated on theseparator in order to improve battery stability.

Representative examples of the gel polymer may include polyethyleneoxide, polyvinylidene fluoride and polyacrylonitrile. When a solidelectrolyte such as a polymer is used as the electrolyte, the solidelectrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte is composed of anon-aqueous electrolyte and lithium.

Examples of the non-aqueous electrolyte include non-protic organicsolvents such as N-methyl-2-pyrollidinone, propylene carbonate, ethylenecarbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate,ethylmethyl carbonate, gamma-butyrolactone, 1,2-dimethoxy ethane,1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran,dimethylsulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, diethylether,formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane,methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane,1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives,tetrahydrofuran derivatives, ether, methyl propionate and ethylpropionate.

Examples of the non-aqueous electrolyte include organic solidelectrolytes such as polyethylene derivatives, polyethylene oxidederivatives, polypropylene oxide derivatives, phosphoric acid esterpolymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol,polyvinylidene fluoride, and polymers containing ionic dissociationgroups.

Examples of the non-aqueous electrolyte include inorganic solidelectrolytes such as nitrides, halides and sulphates of lithium such asLi₃N, LiI, Li₅NI₂, Li₃N—LiI—LiOH, LiSiO₄, LiSiO₄—LiI—LiOH, Li₂SiS₃,Li₄SiO₄, Li₄SiO₄—LiI—LiOH and Li₃PO₄—Li₂S—SiS₂.

The lithium salt is a material that is readily soluble in theabove-mentioned non-aqueous electrolyte and may include, for example,LiCl, LiBr, LiI, LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂,LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li, LiSCN, LiC(CF₃SO₂)₃,(CF₃SO₂)₂NLi, chloroborane lithium, lower aliphatic carboxylic acidlithium, lithium tetraphenyl borate and imide.

Additionally, in order to improve charge/discharge characteristics andflame retardancy, for example, pyridine, triethylphosphite,triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphorictriamide, nitrobenzene derivatives, sulfur, quinone imine dyes,N-substituted oxazolidinone, N,N-substituted imidazolidine, ethyleneglycol dialkyl ether, ammonium salts, pyrrole, 2-methoxy ethanol,aluminum trichloride or the like may be added to the non-aqueouselectrolyte. If necessary, in order to impart incombustibility, thenon-aqueous electrolyte may further include halogen-containing solventssuch as carbon tetrachloride and ethylene trifluoride. Further, in orderto improve high-temperature storage characteristics, the non-aqueouselectrolyte may additionally include carbon dioxide gas and may furthercontain fluoro-ethylene carbonate (FEC), propene sultone (PRS) and thelike.

In a preferred embodiment, the lithium salt-containing non-aqueouselectrolyte can be prepared by adding a lithium salt such as LiPF₆,LiClO₄, LiBF₄, LiN(SO₂CF₃)₂, to a mixed solvent of a cyclic carbonatesuch as EC or PC as a highly dielectric solvent and linear carbonatesuch as DEC, DMC or EMC as a low-viscosity solvent.

Accordingly, the present invention provides a middle- or large-sizedbattery pack comprising the secondary battery as a unit battery.

The middle- or large-sized battery pack has a considerably large batterycell (unit cell) size, as compared to a small battery pack in order toobtain a high capacity and is thus more generally used in the process ofimpregnating an electrolyte or the like. Accordingly, according to thepresent invention, an anode comprising a metal and/or a non-metalcapable of intercalating and deintercalating ions is considerablypreferred in consideration of great reduction in impregnation time.

Preferably, examples of the battery pack include, but are not limitedto, lithium ion secondary battery packs for power storage.

The structure of middle- or large-sized battery packs using a secondarybattery as a unit cell and a fabrication method thereof are well-knownin the art and a detailed explanation thereof is thus omitted in thisspecification.

Now, the present invention will be described in more detail withreference to the following examples. These examples are provided only toillustrate the present invention and should not be construed as limitingthe scope and spirit of the present invention.

Example 1

Graphite having a mean particle diameter of about 20 μm as a corematerial (A), pitch having a carbonization yield of 50% as a materialfor low crystalline carbon (B), and silicon (Si) having a mean particlediameter of about 0.3 μm as a substance (C) capable of intercalating anddeintercalating lithium ions were homogeneously mixed at a weight ratioof A:B:C=90:8:2. This mixture was thermally-treated under a nitrogenatmosphere at 1200□ for 2 hours in an electric furnace. During thermaltreatment, the pitch was softened and carbonized, and at the same time,was coated on a graphite surface in the form of a composite withsilicon, to produce an anode active material coated with acarbon/silicon composite.

The anode active material, SBR and CMC were mixed at a weight ratio ofactive material:SBR:CMC=97.0:1.5:1.5 to prepare a slurry and the slurrywas applied to a Cu-foil to prepare an electrode. The electrode wasroll-pressed to have a porosity of about 25% and punched to fabricate acoin-type half cell. Li-metal was used as a counter electrode of thecell and a coin-shaped battery was obtained using a 1M LiPF₆ electrolytesolution in a carbonate solvent.

Example 2

An anode active material was produced and a coin-type half cell wasfabricated in the same manner as Example 1, except that tin (Sn) havinga mean particle diameter of about 0.3 μm was used, instead of silicon(Si).

Comparative Example 1

An anode active material was produced and a coin-type half cell wasfabricated in the same manner as Example 1, except that only pitch wasused, without using silicon.

Comparative Example 2

An anode active material was produced and a coin-type half cell wasfabricated in the same manner as Example 1, except that pitch andsilicon were mixed at a weight ratio of 1:9.

The carbon yield of the pitch was 50% and the content of the silicon washigher than 90% based on the total amount of carbon and silicon.

Experimental Example 1

Electrolyte impregnation properties of the electrodes fabricated inaccordance with Examples 1 and 2, and Comparative Examples 1 and 2 wereevaluated. The electrode was roll-pressed to have a porosity of about23% and a time for which 1 micrometer of a 1M LiPF₆ electrolyte solutionin a carbonate solvent dropped on the surface of the electrode wascompletely permeated into the surface was measured. Results are shown inTable 1 below.

TABLE 1 Ex. 1 Ex. 2 Comp. Ex. 1 Comp. Ex. 2 Impregnation 92 95 142 93time (sec)

As can be seen from Table 1, the electrodes using an anode activematerial coated with a carbon/metal composite according to Examples 1and 2 of the present invention exhibited considerably short electrolyteimpregnation times, as compared to Comparative Example 1 of electrodeusing an anode active material coated with only carbon. The reason forthis is that the metal surface of the anode active material surface waspartially oxidized and became hydrophilic, enabling the highly polarelectrolyte to be rapidly permeated into particles.

Experimental Example 2

Charge/discharge properties were evaluated using the coin-type halfcells fabricated in accordance with Examples 1 and 2, and ComparativeExamples 1 and 2. Specifically, during charge, the cells were charged ina CC mode at a current density of 0.1 C to 5 mV and then maintained in aCV mode at 5 mV, charging was completed when a current density reached0.01 C. During discharge, the cells were discharged in a CC mode at acurrent density of 0.1 C to 1.5V. As a result, charge/discharge capacityand efficiency of a first cycle were obtained. Then, charge/dischargewas repeated 50 times under the same conditions as above, except thatthe current density was changed to 0.5 C. The results are shown in Table2 below.

TABLE 2 Ex. 1 Ex. 2 Comp. Ex. 1 Comp. Ex. 2 Charge capacity 444.6 411.7385.1 675.0 (mAh/g) Discharge 410.8 380.8 356.6 591.3 capacity (mAh/g)Efficiency (%) 92.4 92.5 92.6 87.6 Capacity 89 88 78 48 maintenance (%)after 50 charge/discharge cycles

As can be seen from Table 2 above, anode active materials coated with acarbon/metal composite according to Examples 1 and 2 of the presentinvention exhibited high discharge capacity and high capacitymaintenance after 50 charge/discharge cycles, as compared to ComparativeExample 1 (anode active material coated only with carbon). The reasonfor this is that a metal material is uniformly distributed as acomposite with carbon on the graphite surface and can realize hightheoretical discharge capacity. Also, a composite in which the metal andcarbon are homogeneously mixed was coated on the graphite surface andelectric conductivity can thus be maintained in spite of variation involume caused by charge/discharge. Also, a part of the metal surface isoxidized and is thus converted into a hydrophilic material performingthe same function as SEI, which forms a strong bond with a core materialvia carbon and thereby inhibits removal of the SEI layer in the repeatedcharge/discharge process. Also, a material having high charge/dischargevoltage is coated, thereby preventing precipitation of lithium andimproving ion conductivity.

Also, when the content of silicon is considerably higher than that ofcarbon as in Comparative Example 2, electrical conductivity wasdecreased, resistance of the electrode was considerably increased, sideeffects of electrolyte were increased and capacity maintenance (%) after50 charge/discharge cycles was considerably low due to great variationin volume of silicon during charge/discharge.

INDUSTRIAL APPLICABILITY

As apparent from the fore-going, the anode active material according tothe present invention is effective in greatly improving a batteryfabrication process, minimizing deterioration in electric conductivityand considerably inhibiting deterioration battery lifespan, through aspecific core/composite coating layer structure and can minimizeperformance and safety problems associated with lithium precipitationthrough presence of material having a high oxidation-reduction level onthe surface of the active material.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

The invention claimed is:
 1. An anode active material for secondarybatteries, capable of intercalating and deintercalating ions, the anodeactive material comprising: a core consisting of a crystallinecarbon-based material; and present on a surface of said core, acomposite coating layer comprising one or more materials selected from agroup consisting of low crystalline carbon and amorphous carbon, and ametal and/or a non-metal capable of intercalating and deintercalatingions, wherein the metal and/or non-metal capable of intercalating anddeintercalating ions is exposed in at least a part of the surface of thecomposite coating layer; wherein the composite coating layer has (i) astructure in which a filler comprising a metal and/or a non-metalcapable of intercalating and deintercalating ions is uniformlydistributed in a matrix comprising one or more materials selected fromthe group consisting of low crystalline carbon and amorphous carbon, or(ii) a structure in which a filler comprising one or more materialsselected from the group consisting of low crystalline carbon andamorphous carbon is uniformly distributed in a matrix comprising a metaland/or a non-metal capable of intercalating and deintercalating ions;wherein an amount of the composite coating layer is 0.1 to 20% byweight, based on the total amount of the anode active material; andwherein a content of one or more materials selected from the groupconsisting of low crystalline carbon and amorphous carbon is 10 to 95%by weight and a content of the metal and/or a non-metal capable ofintercalating and deintercalating ions is 5 to 90% by weight, based onthe total amount of the composite coating layer, and wherein the metaland/or non-metal capable of intercalating and deintercalating ions is atleast one selected from a group consisting of Sn and an alloy of Si andSn.
 2. The anode active material according to claim 1, wherein thecrystalline carbon-based material comprises one or more of graphite andlow crystalline carbon.
 3. An anode mix comprising the anode activematerial according to claim
 1. 4. An anode for secondary batteries inwhich the anode mix according to claim 3 is applied to a currentcollector.
 5. A secondary battery comprising the anode for secondarybatteries according to claim
 4. 6. The secondary battery according toclaim 5, wherein the battery is a lithium secondary battery.
 7. Abattery pack comprising the secondary battery according to claim 6.